Electrostatically assisted intaglio printing



Nov. 11, 1969 G, ADAMSON ETAL 3,477,369 ELECTROSTATICALLY ASSISTEDINTAGLIO PRINTING Filed May 4, 1967 5 Sheets-Sheet 1 INVENTORS ROBERT G.ADAMSON CHARLES H. ANGELL JAY C. ROOTE JOEL E HUTCHISON DANIEL A.COBERLEY' Nov. 11, 1969 R, ADAMSON ETAL 3,477,369

ELECTROSTATICALLY ASSISTED INTAGLIO PRINTING Filed May 4, 1967 5Sheets-Sheet z INVENTORS ROBERT s. ADAMSON CHARLES H. ANGELL JAY c.ROOTE 2 w JOEL F. uurcmson DANIEL A. COBERLEY Nov. '1 ,1 19 R. G.ADAMSON ETAL 3,477,369

ELECTROSTATICALLY ASSISTED 'LN'IAGLIO PRINTING Filed ,May 41, 1967 5Sheets-Sheet a INVENTORS ROBERT 6. ADAMSON CHARLES H. ANGELL JAY C.ROOTE JOEL F. HUTCHISON DANIEL A. COBERLEY BY I W q/ Nov. 11, 1969 R. G-ADAMSON ETAL 3,477,369

ELI'JCTROSTATICALLY ASSISTED INTAGLIO PRINTING Filed May 4, 1967 5Sheets-Sheet Q INVENTORS ROBERT o. ADAMSON CHARLES H. ANGELL JAY c.ROOTE JOEL F. uu'rcmsou DANIEL COBERLEY Q BY I I parwas United StatesPatent US. Cl. 101-153 6 Claims ABSTRACT OF THE DISCLOSURE The inventionis directed to means for electrostatically assisting the transfer of inkfrom a pattern thereof on a printing cylinder to a web of substantiallynon-conductive material, such as paper, paper board, plastic film andthe like, as the web passes between and in contact with the printingcylinder and an impression cylinder.

A covering of electrically conductive, resilient material is provided onthe cylindrical surface of the impression cylinder, and a layer ofelectrical insulating material is disposed between said conductivecovering and the cylindrical, metallic body of the impression cylinder.A source of relatively high voltage current is provided and connectedwith an electrically conductive member which is insulated from shortcircuiting the current to ground and which bears directly upon saidconductive covering on the impression cylinder, thus establishing adifference in potential from said covering, through the web to theprinting cylinder, which is grounded, to polarize the ink on theprinting cylinder and attract it to the web.

The invention also provides safety devices for preventing the furtherflow of current from said source to said conductive member when itreaches a preselected value and for preventing current flow to theconductive member until the impression is made and the printing andimpression cylinders have reached a predetermined rotational speed.Current flow to the conductive member is also discontinued automaticallyin case of a break in the web.

When the length of the printing and impression cylinders exceed thewidth of the web, a relatively thin covering of high dielectric materialmay be provided over the portion or portions of said conductive coveringon the impression cylinder which extend beyond one or both edges of theweb and, preferably, such portion of the conductive covering is thinnerthan the remaining portion covered by the web, by an amount equal to orslightly more than the thickness of said dielectric material.

When an additional, relatively rigid metal cylinder is required to backup the impression cylinder and prevent its flexing, the cylindricalsurface of the back-up cylinder is also covered by a relatively thincoating or sheet of high dielectric material.

The printing industry has long sought an effective and economical methodand means of printing by applying an electrostatic charge to pigmentedfluid and attracting it to a running web of paper or the like to form apredetermined, repetitive, pigmented pattern on the web. Most of theefiorts along these lines have undertaken to avoid the use of a printingimpression (i.e., positive physical contact between the web and aprinting cylinder or simi lar element carrying the pigment) and haveundertaken to attract the pigment to the web through a small air gapionized by an electrostatic charge. Such concepts do not lend themselvesto the use of liquid inks or dyes but require relatively light andfinely divided dry pigments having low cohesive and adhesive properties,so that they 3,477,369 Patented Nov. 11, 1969 will flow readily and canbe attracted to the web across the air gap. While some experimentalprogress has been made along these lines, such methods have had littleor no commercial impact in publication and package printing, primarilybecause of their experimental nature, questionable advantage overconventional printing and the highly special and rather costly andcomplex equipment required.

Recent experimental work and tests, initiatedby the Gravure ResearchInstitute and continued by the firm to which this application forLetters Patent is assigned, have been directed along lines quitedifferent from those above mentioned. This work has contemplatedutilization of the many hundred existing high-speed, web-fed presses inuse, without extensive or costly modification, and the use ofconventional liquid inks and commonly used grades of paper, paperboard,plastic film, and laminates of such materials. It deliberately makes useof a printing impression or nip which induces some transfer of ink tothe web as it is propelled between an impression cylinder and aconventional printing cylinder which carries the inked pattern to beapplied to the web. However, it permits the use of lighter impressionpressures than normally required in conventional printing, since the inktransfer is materially augmented and improved by the application of anelectrostatic charge.

'In accordance with the features of the present invention, a source ofrelatively high voltage, low amperage direct current is provided. Aterminal of one polarity (preferably but not necessarily the positivepole) is connected and supplies regulated electrical energy to an outercovering of conductive, resilient material provided on the impressioncylinder. This conductive outer covering is prevented fromshort-circuiting the current to the frame of the press or to otherconductive structureby a layer of dielectric material provided betweenthe cylindrical metal shell or core of the impression cylinder and theaforesaid outer covering. The metal printing cylinder is grounded (orconnected to that terminal of the power supply of opposite polarity tothat connected to said conductive outer covering), so that a diiferencein potential is established between the impression and printingcylinders through the web which is in contact with both cylinders. Theresulting electrostatic charge applied to the ink, in the patternthereof on the printing cylinder, attracts it to the web and materiallyimproves its transfer.

In a conventional web-fed printing press, the printing and impressioncylinders normally rotate at relatively high speed. The printingcylinder is journaled in bearings mounted on or in the frame of thepress, which, in the practice of the invention, adequately grounds thiscylinder, so that it is convenient to employ this arrangement, leavingthe printing cylinder at ground potential. This necessitates applying apositive charge on the impression cylinder and, to establish adifference in potential through the web to the printing cylinder, thecharge on the impression cylinder must not be dissipated to ground viaits metal core or shell, shafts and bearings, and the frame of the pressor other supporting structure. V

Conventionally, the impression cylinder shafts are journaled in avertically movable, metal framework which slides on ways which are apart of the press frame. This presents a serious problem in establishingthe necessary difference in potential between the impression andprinting cylinders, and preventing-short-circuiting of the chargeapplied to the impression cylinder. It is overcome in the presentinvention by making the resilient outer covering of the impressioncylinder electrically conductive, insulating this covering from themetal shell or core of the cylinder, and applying the charge directly tothe surface of the conductive covering. In the preferred embodiment ofthe invention, this is accomplished by providing an idler roller,bearing directly on the conductive outer covering of the impressioncylinder at a location circumferentially displaced from the nip betweenthe impression and printing cylinders. This relatively lightweight idlerroller is journaled in suitable bearings carried in spring-loadedmounting blocks secured to but electrically insulated from the aforesaidsliding framework in which the impression cylinder is journaled. Thusthe idler roller moves up and down with the impression cylinder as thelatter is lifted and lowered to part or make the impression.

The above described and other details of the invention, including themeans by which the idler roller is connected with the power supply, areillustrated in the accompanying drawing, which will be later described.

While some or all of the features of the invention will be foundadvantageously applicable to other than rotogravure printing, such asstereotype or letterpress, planographic or offset, fiexographic(formerly known as aniline printing) and the various hybrid forms suchas letterset or dry offset, gravure offset, etc., they are particularlydesirable in intaglio or gravure printing and the subsequentillustrations and description will be addressed primarily to this typeof operation.

Intaglio or gravure printing is particularly needful of the subjectsystem because of the difficulty often encountered, in conventionalpractice, of adequately and uniformly emptying the small etched orengraved cells which make up the dot structure of the pattern in which Uthe ink is carried. This difficulty causes what are known as skippeddots in the printed pattern on the web, particularly in lightlypigmented and delicately shaded areas of the copy. This may also bequite noticeable in darker and denser areas. The augmented ink transferaccomplished with the subject system largely overcomes this difficultyand results in greatly improved appearance of the printed copy.

On relatively rough stocks, such as uncoated and lightly calendered oruncalendered papers produced from ground wood pulp, for example, andalso on the typically rough surfaced and relatively unyielding paperboards widely used in package printing, the improvements resulting fromuse of the subject system are surprisingly noticeable, even to theunpracticed eye. Both monotone and multicolor work are materiallyimproved. Greatly improved results are obtained on practically any typeand grade of printing stock, and the system has the advantage ofproviding good reproductions on cheaper stocks than would otherwise berequired for acceptable work. It also permits the use of lighterimpression pressures than otherwise normally required for acceptableprinting. The use of lighter impression pressures saves wear,maintenance and replacement of bearings and other load-carrying members,and prolongs the useful life of both the printing cylinders and theresilient covering of the impression cylinders.

Initial attempts to assist gravure printing by the use of anelectrostatic charge were rendered hazardous by fact that gravure inksare light (e.g., of relatively low viscosity) compared with those usedin other types of printing, and normally contain a high percentage offlammable hydrocarbon solvents of low volatility. Numerous fires wereencountered and, in the absence of precautionary measures, it ispossible to cause an explosion. Purging systems, intended to keep thehydrocarbonair mixture in the vicinity of the impression below flammableproportions, sometimes aggravate rather than help the situation,presumably on account of the turbulence created in this area. However,We have found that the ignition hazard can be avoided by limiting thecurrent drawn at the nip or impression to a low value of the order of1.5 to 3 milliamperes. To insure that it does not exceed a safe value,provision is made in the power supply circuit provided by the invention,for quickly shorting the output of the power supply to ground when thecurrent drain reaches a predetermined, adjustable maximum value.

The invention also incorporates other safety features which Will bedescribed in conjunction with the accompanying drawing.

In the accompanying diagrammatic drawings, FlG. 1 is an elevational viewshown, partially in cross section, of one printing unit of a rotogravurepress incorporating the invention.

FIG. 2 is a sectional elevation of the same press unit, taken along line22 in FIG. 1.

FIG. 3 is an enlarged detail, shown partially in cross section, of oneend of the conductive idler roller, and its bearing and bearing housing.

FIG. 4 is an enlarged longitudinal view, shown partially in crosssection, of an end portion of the impression cylinder in FIGS. 1 and 2.

FIG. 5 is an end view of the impression cylinder shown in FIG. 4.

FIG. 6 is an enlarged detail, shown principally in cross section, of anend portion of an impression cyl nder provided with a modified form ofthe dielectric and resilient conductive coverings shown in FIG. 5.

FIG. 7 illustrates the general arrangement of a printing cylinder,impression cylinder, back-up cylinder, and the idler roller on aprinting unit utilizing the invention.

FIG. 8 is a circuit diagram of the power supply and associated elementsprovided by the invention.

In FIGS. 1 and 2, the substantially conventional portions of therotogravure printing unit here illustrated comprise a printing cylinder1 and an impression cylinder 2, between and in contact with which theweb 3 to be printed upon is propelled in the direction indicated by thearrows. The printing cylinder is driven through suitable gearingindicated at 4 in FIG. 1, and its lower portion is immersed in a pool 5of ink. An intaglio pattern of the printing to be applied to the web isnormally etched into the gravure printing cylinder and consists ofcloselyspaced minute depressions or cells which are substantially filledwith ink as the printing cylinder passes through the pool. Since theentire cylindrical surface of the gravure cylinder is wetted with ink byimmersion therein, the excess (i.e., that not contained in the intagliopattern) is wiped or doctored from the cylinder by a doctor blade 6before it reaches the impression or nip, indicated at '7, formed betweenthe printing and impression cylinders.

A portion of each of the side frames of the press is indicated at 8. Thegravure cylinder 1 is journaled at its opposite ends in bearings 9 insuch manner that the assembly, including the cylinder 1, bearings 9,bearing housings, and splined shaft 10, which connects the cylinder withthe drive gearing, may be readily removed for replacement or reworkingof the cylinder to apply a different pattern of printing.

To assist removal and replacement of the gravure cylinder and, whendesired, the impression cylinder as well, the latter is lifted bysuitable double-acting hydraulic cylinders attached to shafts 11, butnot shown in the drawing. The hydraulic cylinders also lower theimpression cylinder and exert pressure between the printing andimpression cylinders in the nip area 7 when the impression is made(i.e., when the impression cylinder is down). At times during operationof the press and for a variety of reasons, the impression may be partedby lifting the cylinder 2, as, for example, while the web is beingthreaded through the press or in case of a Web break. This permitsrotation of the gravure cylinder to keep it wetted and prevent drying ofthe ink thereon while there is no web passing through the impressionand, otherwise, until it is desired to start printing.

To accommodate lifting and lowering of the impression cylinder, it isjournaled at its opposite ends in suitable bearings, not shown,contained within the bearing housings 12 which are detachably secured toa framework 13 to which the shafts 11 are attached. This frame 13 slidesvertically on ways 14 which are a part of or are secured to the pressside frames 8.

The arrangement illustrated and above described, or its functionalequivalent, is employed on all web-fed, rotogravure presses and asimilar arrangement is used on most other types of web-fed presses.

Since, in conventional practice, the entire printing press is mounted ona heavy foundation of reinforced concrete and the framework, cylindershells, shafts, bearings, gearing, etc., are constructed of steel orother metals or alloys, the entire structure is electrically conductiveand is at ground potential. The features of the present invention whichwill now be described are designed to obviate the difiiculties, arisingfrom this conventional printing press construction, in undertaking toapply a controlled electrostatic charge in the nip area and in reducingor eliminating the hazard of fire and explosion when vapors from the inkmay create this hazard.

In the embodiment of the invention shown in FIGS. 1 and 2, anelectrically conductive idler roller 15, is attached to the slidingframe 13 to which the impression cylinder 2 is also secured, so that theroller 15 bears directly upon the surface of the impression cylinder andmoves with the impression cylinder as the latter is lifted and lowered.The means of such attachment here illustrated (see FIG. 1) include amounting bracket 16, one portion 17 of which is interposed between thebearing housing 12 for the impression cylinder 2 and the sliding frame13, these members being firmly bolted and pinned together, as shown.Another portion of the mounting bracket 16 is an angle-shaped member 18'in which a hearing housing 19 is slidably mounted by means of theshoulder bolts 21 and slots 22 (see FIG. 2). The bearing housing 19 isspring-loaded, as indicated at 23, to urge it into firm contact with theimpression roller 2. This housing 19 and its cover cage the bearing 24,into which the shaft 25 of the idler roller extends and, to electricallyinsulate the idler roller from the press frame, these members 19 and 20are made of material having good dielectric properties. Suitablematerials for this purpose, which combine sufiicient tensile andcompressive strength with dielectric properties, include laminatedfabrics impregnated and bonded with phenolic resins, tempered hardboard,and other materials having similar properties.

It will be understood that a mounting such as above described isprovided at each end of the idler roller. From at least one of theseassemblies, a wire or similar electrical conductor, covered with hightension insulation and indicated at 26, is connected to the positiveterminal of a power supply such as shown in FIG. 8. Within the assemblythis conductor is connected, as indicated in FIG. 3, with anotherconductor secured to the bearing housing within a cavity 31 provided inthe housing on the outboard side of bearing 24. A drive screw 32, in thecase illustrated, secures one end of conductor 30 to housing 19, in linewith the axis of rotation of the idler roller 15, and has awear-resistant head 33 of hardened steel or hard chrome-plated steel,for example. The head 33 bears upon a spring-loaded electricallyconductive plunger 34 which isretained by shoulder 35 in a bolt 36drilled to receive the plunger 34 and spring 37. Preferably, plunger 34is made of or plated with copper, silver, or other highly conductive,relatively soft metal which will form good contact with the button orhead 33. The head of bolt 36 is recessed in the counterbored end ofshaft 25 and a tapped hole in the shaft retains the threaded portion ofthe bolt. This or other functionally equivalent arrangement is employedto conduct current from the power supply to the idler roller as thelatter is rotated by its contact with the rotating impression cylinder.

Friction and wear between the conductive element and the surface ofimpression cylinder 2 are minimized by the use of a roller as theconductive element. We do not wish to limit the invention to thisarrangement nor to the specific construction shown and described, sinceother means of applying current from the power supply to the impressionroller will be readily apparent. However, a construction and arrangementof this general nature, which provides rolling contact with the surfaceof the impression cylinder, is preferred.

Referring to FIGS. 4 and 5, the cylindrical metal shell of theimpression cylinder 2 is indicated at 40 and is closed at each end bymembers which. include the bearing journals, one of these members beingshown at 43.

Extending over the length of the metal shell and bonded thereto is alayer 41 of material of good dielectric strength which insulates theshell from the outer conductive covering 42. The insulating layer may bea compound of natural rubber, one of the synthetic elastomers orsuitable thermoplastic insulation, preferably of the type and grade usedfor high tension insulation on wires and cables. It is selected for goodbonding to the shell 40, which is ordinarily steel, as well as to theresilient conductive covering 42 and for good dielectric strength,preferably in a thickness of the order of to The resilient outercovering 42 is preferably a compound of rubber or other elastomercontaining sutficient carbon black, or the like, to give it anelectrical conductivity of the order of 10 to 10 ohm-centimeters andhaving a durometer reading of from about 60 to about by the Shore Ascale.

In general, aside from having reasonable conductivity, the resilientcovering 42 may have other properties substantially corresponding to theresilient impression roll covering conventionally employed on theparticular press with which it is used. As in conventional practice,this material may be built up (laminated) to a thickness of from to fromsheet material of lesser thickness, with the laminations vulcanized orotherwise bonded to form a homogenous covering. The outer surface iscarefully ground, usually with a slight crown at the center, taperingevenly to the ends of the cylinder. A substantial thickness of the orderof /8" to A5" permits several regrindings when the surface begins todeteriorate due to prolonged use or damage.

It will be noted that, as shown in FIG. 4, the end portions 41E of thedielectric layer 41 are thicker than its intermediate portion, theseends being ground to the same outside diameter as the outer covering 42.The reason for this is that the impression cylinder and the printingcylinder are usually somewhat longer than the widest web which the pressis intended to handle. By making the length of the conductive covering42 slightly less than the web width (say about /2" less), it will becompletely covered by the web under normal conditions and the insulatedend sections 41E, which extend beyond the edges of the web, will preventshort circuiting of the charge in the conductive covering to ground bycontact with the bare end portions of the printing cylinder. In FIG. 4,the approximate position of the edge of the Web is indicated by the lineW.

As an alternative to the use of insulated end sections 41E, or in case aweb of less than maximum width is sometimes employed, a construction;such as illustrated in FIG. 6 may be used. In FIG. 6, the metal shell ofthe impression cylinder is again designated as 40, the dielectric layer41 and the conductive outer covering 42. The approximate position of theadjacent edge of the web is again indicated by the line W. In thisembodiment, the conductive covering 42 preferably is undercut on itsouter surface for a distance extending slightly say A" to /2", insidethe length which will be covered by the web and over this undercutportion a relatively thin covering 44 of material of high dielectricstrength is applied. This material may conveniently be a seamless sleeveof one of the substances, such as fluorocarbon resins, for example,which can be slipped over the end of the cylinder and shrunk securely inplace by the application of heat.

Of course, an insulating covering, such as shown in FIG. 6, may also beused in combination with a section 41B such as shown in FIG. 4. Ineither case, the depth of the undercut in the outer layer 42 preferablyis the same or slightly more than the thickness of the dielectriccovering 44, after the latter is in place on the cylinder, so that it isunnecessary to grind the covering 44 to the same outside diameter as thecovering 42. In some instances a good grade of electrical tape may bewrapped about the end of the cylinder without undercutting the covering42, providing the compressibility of the materials at the thus coveredends of the cylinder permit sufiicient impression or nip between theimpression and printing cylinders 'in the area covered by the web.

Many printing presses designed to accommodate web widths greater thanabout 48", for example, avoid the necessity of employing the massive andrigid impression cylinder construction, which would otherwise berequired, by providing a relatively heavy, rigid back-up roller toprevent flexing of the impression cylinder. The primary reason for thisis that the impression cylinder must occasionally be removed forreplacement and/ or regrinding of the resilient covering and it isdesirable to keep the cylinder light enough to permit ready removal andhandling. A back-up cylinder, on the other hand, ordinarily does nothave to be removed and can be of solid construction, similar to calendarrolls used in papermaking. FIG. 7 diagrammatically illustrates thenormal cylinder arrangement in a press employing a back-up roller.

In applying the subject system to a press having the cylinderarrangement shown in FIG. 7, the back-up roller 70, which is of heavymetal and, therefor conductive, is given a coating 71, on itscylindrical surface, of dielectric material which insulates the metalcore or shell 72 to prevent current leakage or short circuiting from theimpression cylinder.

In FIG. 7, the printing cylinder, impression cylinder, and the web aredesignated by the same reference numerals as used in the other figuresof the drawing, namely 1, 2, 3, respectively. The impression cylindermay be covered in the same manner as above described in connection withFIGS. 4 and 5, or as described in connection with FIG. 6. However, sincethe back-up roller occupies a position on the impression cylinderdiametrically opposite the position of the printing cylinder, theconductive idler roller, which in this case is designated as 73,occupies a different position and is conveniently mounted in a differentmanner, as will be later described.

Since the backup cylinder 70 is difficult to remove from the press, thedielectric coating 71 is preferably painted or sprayed on this cylinderwhile it is in place, when the subject system is applied to an existingpress of this construction. Suitable liquid coatings, which may besprayed or brushed onto the surface of the back-up cylinder and cured toa well-adhering film by heating or by catalytic action, are availablefrom several sources under different trade names. Usually, these are areepoxy resins to which a suitable catalyst is added before application.Such materials are particularly suitable for the purpose here intended,because they readily bond to the metal cylinder, have good dielectricproperties, and are resistant to the solvents used in gravure inks.

A suitable alternative coating for the back-up cylinder, which also maybe applied with the cylinder in place in the press, consists of two ormore wrappings of plastic film having gOOd dielectric strength. At leasttwo such wrappings are recommended in order that the ends of each wrapmay be butted and the abutted joints in alternate wraps displaced fromeach other about the circumference of the cylinder. Tetrafluoroethyleneand similar fluorocarbon resins in sheet form are examples of suchmaterial.

In the case illustrated in FIG. 7, the idler roller 73 is supported onarms 74, disposed at opposite ends of the roller, and pivoted about theend shafts 75 of the back-up roller 70. The hub of each of the arms 74,

which bears upon the shaft 75, is preferably divided, as indicated at76, to accommodate a removable cap 77, which is secured to the otherportion of the hub by bolts, not shown. This construction, or itsequivalent, permits mounting the idler roller on the press withoutremoving the backup roller. The weight of the arms 74 and the idlerroller will normally be sufficient to hold the idler roller in firmcontact with the resilient, conductive surface of the impressioncylinder 2, and when mounted as shown, with reference to the directionof rotation of the back-up roller, this will also assist in maintaininggood contact between idler roller 73 and impression cylinder 2.

A suitable end closure, indicated at 78, at one or both ends of theidler roller shaft, accommodates a contact arrangement of the samegeneral type shown in FIG. 3, to which the conductor 26 from the powersupply is attached.

Referring now to FIG. 8, which is essentially a circuit diagram, it alsoshows in diagrammatic form the printing cylinder 1, impression roller 2,web 3, and idler roller 15, to indicate how the circuit between theseelements and the source of power for the subject system is connected andcompleted. Certain elements and subassemblies in the circuit of thepower supply and its associated parts are of Well-known construction andthey function, individually, in a well-known manner. To avoidunnecessary complexity in the diagram, these wellknown subassemblies areshown in block form.

Readily available A.C. line current (such as 115 v., 60 cycle, forexample, atlhough other voltages and frequencies may be used) issupplied to low-voltage, full-Wave rectifier 80 having, for example, anoutput of +50 volts D.C. This low-voltage D.C. is supplied to thevoltage regulator 81, which is essentially a three-stage transistoramplifier with an internal source of reference voltage, such as abattery, and a regulating feed-back which will be later described. Theregulated low-voltage D.C. output is fed to the D.C.-to-D.C. transistorinverter-rectifier 83, where, in accordance with well-known practice,the low voltage DC. input is first converted into high-frequency,high-voltage square waves, in the inverter section. Theinverter-rectifier assembly also contains a bridge-type rectifiersection wherein the high-voltage square waves from the inverter sectionare converted to high-voltage direct current.

The positive output side of the inverter-rectifier is connected, asdiagrammatically shown in FIG. 8 and described in more detail withreference to FIG. 3, to the idler roller 15. The negative side of theinverter-rectifier output is connected to ground through potentiometerP2 and meter M2. The printing cylinder 1 is also grounded to completethe circuit and provide energy for electrostatically assisting thetransfer of ink as previously described.

The circuitry provided and illustrated in FIG. 8 makes provision for thefollowing automatically-controlled safety features:

(1) Temporarily interrupting operation of the system whenever the loadwhich it imposes on the power supply exceeds a preselected safe limit.

(2) Discontinuing operation of the system until it is intentionallystarted after clearing the difficulty, when it imposes a persistent orfrequently recurring load on the power supply.

(3) Preventing operation of the system until the press reaches apredetermined operating speed (i.e., cylinder r.p.m. or linear webspeed).

(4) Preventing operation of the system until the impression is made(i.e., the impression cylinder has been brought into firm contact withthe printing cylinder).

The aforementioned safety provisions and their mode of operation areexplained in conjunction with the following description of the sequenceand mode of operation of the circuit components.

The aforementioned A.C. supply line has a main disconnect switch S1 and,with this switch closed, the line is connected with the low-voltageA.C.-to-D.C. rectifier 80. The supply line is also connected withanother rectifier 83 of the same type to provide volts DC, for example,which is used as will be later described. Also, the A.C. power line isconnected with a transformer T3 which provides a suitable filamentvoltage to the Thyratron tube V1.

As current flows through the Thyratron filament circuit from transformerT3, the current sensitive relay coil K1 is energized. This closes thecorresponding contacts K1 of the relay to connect the negative side ofthe output from rectifier 83 with the time delay unit 84, whichfunctions in the following manner to prevent energization of the rest ofthe system until the filament of the Thyratron tube warms up and rendersthis tube operative.

With contacts K1 closed, the capacitor C11 in the time delay unit startscharging from voltage drawn through relay coil K2 and the resistors R16and R18. As soons as the voltage of capacitor C11 has risen to asuificient value to cause the unijunction transistor Q7 to conduct, theresulting positive pulse of voltage generated at its unijunction base isapplied to the gate of SCRl, turning it on. Conduction through SCRlpermits sufficient voltage to be applied to relay coil K2 to causeoperation of this relay, closing its contacts K2A and K2B in a branch ofthe A.C. supply line. Until this happens, the pushbutton PB1, the relaycontacts K6 and the relay contacts K7 in the aforesaid branch line arerendered ineffective to close the circuit of this branch line by virtueof the open contacts at K2A and KZB.

The function of the momentary contact pushbutton FBI is to initiate thesystem operation, but until relay contacts KZA, K2B, K6 and K7 are allclosed, no energy can be transmitted through the branch line in whichthese contacts are located, and the pushbutton PBl remains ineffective.The manner in which contacts K2A and KZB are closed has been describedabove. The manner in which contacts K6 and K7 may also be closed, sothat the system operation can be initiated by pushbutton PB1, will nowbe described.

When the impression cylinder 2 is lowered into contact with the printingcylinder, as shown at the right hand side of the diagram, the contactsof limits switch S2 will close. This causes power from the A.C. supplyline to energize relay coil K6, closing the corresponding contacts K6After the press is started in the usual manner, not illustrated, theprinting cylinder is accelerated to the desired running speed throughthe drive shaft 86 and the conventional gearing indicateddiagrammatically at 87. A suitable speed sensitive switch which, for thesake of simple illustration, is here shown as a device 88 similar to aflyball governor attached to drive shaft 86 and having contacts 89,closes these contacts when cylinder 1 reaches a predetermined speed.Closing contacts 89 completes the circuit through relay coil K7,energizing the same to close the corresponding relay contacts K7 Withrelay contacts K2A, KZB, K6 and K7 all closed, the impression betweencylinders 1 and 2 will have been made, the cylinders will be rotating atthe desired speed and the time delay unit 84 will have functioned toinsure that the Thyratron V1 is ready to operate. The system is thusready to start supplying power to the idler roller 15. By then manuallyoperating pushbutton PB1, to close its contacts, this will complete theclosing of the entire series of contacts in the branch A.C. supply lineand relay coil K4 will energize to close the contacts K4A and K4B.Contacts K4A remain closed after pushbutton FBI is released, thuskeeping the aforesaid branch line conductive until the stop button PB2is pushed or one of the series of other contacts in the branch line dropout.

When contacts K4B close, the DC. output from rectifier 80 enters thevoltage regulator 81 and the latter supplies 10 its regulated output tothe inverter-rectifier 82. Meanwhile, since contacts K2A, K6 and K7 haveclosed, the relay coil K5 has become energized to close its contacts atK5 which connects the positive output terminal of the inverter-rectifierwith the idler roller 15. Its corresponding negative terminal isconnected to ground, as will be later described, to complete the circuitfrom the inverterrectifier through the idler roller 15, web 3, andprinting cylinder 1 to ground, and return to the inverter-rectifier.

A portion of the positive output from the inverterrectifier is lead toground through resistor R19, microammeter M1, which measures voltage,and potentiometer P1, A sample voltage, the value of which depends uponthe setting of wiper arm of potentiometer P1 and which is positive withrespect to ground, is picked from the potentiometer and fed back to thevoltage regulator 81. Here the sample voltage is compared. in a bridgecircuit with the aforementioned reference voltage in the regulator andthis comparison initiates an impedence change in the input to theinverter-amplifier from the regulator to bring the sample and referencevoltages to equilibrium. Thus, changing the setting of the wiper arm ofthe potentiometer P1 changes the proportion of the voltage fed back tothe regulator and causes the latter to alter its high voltage output tothe idler roller 15. Meter M1 indicates the voltage level selected.

Preferably, the voltage to the idler roller 15 may be adjusted over awide range, to accommodate printing stocks of different resistivity,depending upon the caliper (thickness), structure, etc. For example,uncalendered newsprint of about 32 to 34 pounds basis weight may requireonly about 800 volts into the idler roller to obtain good ink transfer.On the other hand, paperboard of from 20 to 40 mils thickness mayrequire from 2,000 to 5,000 volts.

The negative output terminal of the inverter-rectifier is connected toground through potentiometer P2 and meter M2. Since all load currentflows through this circuit, meter M2 monitors the actual current drawnby the system and applied to the printing operation. To prevent thiscurrent from reaching a dangerously high level, which can happen, forexample when web 3 breaks or when holes in the web pass through theimpression, provision is made for limiting the current drawn by theidler roller 15 and shorting the inverter-rectifier output to ground ifand when the current level becomes excessive. To accomplish this, partof the voltage dro across potentiometer P2 is picked off by the wiperarm and applied to the current sensor 85. The current sensor functionsas follows.

If and when the current flowing through potentiometer P2 reaches a levelat which the voltage at the wiper arm setting exceeds the thresholdvoltage of the Zener diode D3, to which this pick-oif voltage isapplied, the transistor Q6, to which the diode is connected as shown,conducts and grounds the grid of Thyratron V1. This causes the Thyratronto conduct heavily (crowbar) and effectively short circuit the highvoltage output of the inverter-amplifier to ground through theThyratron.

In addition, when transistor Q6 conducts to trigger the Thyratron, thecoil of relay K3 will be energized to open the relay contacts K3 andinterrupt the rectified low voltage supply to the voltage regulator.This, of course, turns off the inverter-rectifier and, when its highvoltage output decays to zero, Thyratron V1. ceases to conduct, nocurrent passes through the current sensor and, with relay coil K3 thusde-energized, relay contacts K3 drop back to closed position. If thecause of the amperage surge has meanwhile been corrected or cleared, thesystem is then back in operation. If the fault persists or is repeated,the above described cycle is repeated.

When relay coil K3 is energized, relay contacts K3 are closed toconnecta counter with the A.C. supply line. Counter 90 is of the typewhich closes an internal contact when a selected count is reached andcounts one digit each time relay contacts K3 close. When the countreaches the preselected number, say three or five, for example, theinternal contact completes the circuit from the A.C. supply line throughrelay coil K8, energizing the same to open the normally closed contactsK8 in the branch A.C. supply line. This de-energizes relay coil K4,causing contacts K4A and K413 to open and thereby discontinuing theoperation of the system until pushbutton PB1 is manually operated. Thus,if there is a persistent heavy drain of current or this condition isrepeated for a number of times corresponding to the preselected numberon the counter, the current supply to tthe idler roller is discontinueduntil operation is intentionally renewed, giving the operator anopportunity to find and correct the difiiculty. When desired, a warning,such as a light or audible signal, may be turned on automatically whenthe counter reaches the preset count, and/ or operation of the press maybe stopped automatically.

Since the Thyratron tube V1 is depended upon to ground the output of theinverter-rectifier in the event of an excessive current drain, provisionis made for deenergizing the system in case the Thyratron filamentfails. In this event, the current through relay coil K1 collapses,causing contacts K1 to open and disconnect the time delay unit 84 fromthe rectifier 83. This de-energizes relay coil K2, causing its contactsKZA and K2B to open, thus de-energizing relay coil K4 and opening itscontacts K4A and K4B, which shuts down the system and returns allcircuits to their initial inoperative condition.

It should be noted that, in FIG. 8, all relay contacts are shown withthe corresponding coils in de-energized condition.

While the foregoing description and the drawings deal with only a singleprinting unit, it will be apparent that, on multiple unit presses, thesubject system may be applied to all printing units or to as many asdesired. It will also be apparent that numerous modifications of thespecific embodiments illustrated and described may be made withoutdeparting from the spirit, scope and teachings of the invention.

We claim:

1. Means for assisting the transfer of ink, carried in an intagliopattern on a metal printing cylinder, to a web of substantiallynon-conductive material as the latter passes through a nip between theprinting cylinder and a resiliently covered metal impression cylinder,comprising the combination of:

an outer covering of resilient material on said impression cylinderhaving a resistivity of the order of ohm-centimeters to 10ohm-centimeters, the external peripheral surface of said outer coveringcontacting the substantially non-conductive material of the web at thenip between the printing cylinder and the impression cylinder,

a layer of dielectric material having a resistivity substantiallygreater than that of said outer covering disposed between said outercovering and the metal of said impression cylinder,

an electrically conductive contact element in physical contact with theexternal peripheral surface of said outer covering of said impressioncylinder at a region about the periphery of said impression cylinderremote from said nip, and

an electric circuit connected with said electrically conductive contactelement for applying a direct current electrical potential between saidelectrically conductive contact element and said printing cylinder withthe potential applied by said contact element being transmitted byelectric current flow in a circumferential direction through thematerial of said outer covering of said impression cylinder from theportion of said outer covering instantaneously in contact with saidcontact element to the portion of said outer covering instantaneously incontact with the substantially non-conducting material of said web atthe nip, said layer of dielectric material insulating said outercovering from the metal of said impression cylinder and the appliedpotential maintaining said outer covering and said printing cylinder atopposite polarities to charge the ink in said pattern to a polarityopposite to that of said outer covering for attraction of the ink to theweb at the nip between the printing cylinder and the impressioncylinder.

2. The combination of claim 1 with a transistor circuit having an inputconnected to said electric circuit for receiving an input signal inaccordance with the current drawn at the nip between the printingcylinder and the impression cylinder and having an output for supplyingan output signal when the current drawn at the nip eX- ceeds apreselected value, and means connected with the output of saidtransistor circuit and controlled by said output signal therefrom todiscontinue the flow of current to said outer covering when the currentdrawn at the nip exceeds said preselected value.

3. The combination of claim 1 with thyratron means connected to saidelectric circuit and shiftable to a conductive state to discontinue theflow of current to said outer covering, and a current sensor responsiveto current flow in said electric circuit and controlling conduction ofsaid thyratron means, said current sensor including Zener diode meansreceiving an input voltage proportional to current flow in said electriccircuit and having a threshold voltage which must be exceeded before thethyratron means is shifted to its conductive state.

4. The combination of claim 1 with said electric circuit having meansfor limiting the current drawn at the nip between the printing cylinderand the impression cylinder to a value of the order of 1.5 to 3milliamperes.

5. The combination of claim 4 with said electric circuit applying anelectrical potential of about 800 volts between said electricallyconductive contact element and said printing cylinder.

6. The combination of claim 4 with said electric circuit applying anelectrical potential of about 2,000 volts between said electricallyconductive contact element and said printing cylinder.

References Cited UNITED STATES PATENTS 162,650 4/1875 Hinchclifil0l4l6.1 2,141,403 12/1938 Olfen 101--416.1 XR 2,212,820 8/1940 Barber10l153 2,520,504 8/ 1950 Hooper 101-426 2,558,900 7/1951 Hooper 101--426XR 2,558,901 7/1951 Hooper 101-2l9 2,590,321 3/1952 Huebner 101-1163,295,441 1/1967 Garnier 10l335 3,339,484 9/1967 Pannier 101-219 EDGARS. BURR, Primary Examiner US. Cl. X.R. 101--170

